EP0026275A2

EP0026275A2 - Printer having a print ribbon feed device

Info

Publication number: EP0026275A2
Application number: EP80103960A
Authority: EP
Inventors: James Michael Rigotti
Original assignee: International Business Machines Corp
Current assignee: International Business Machines Corp
Priority date: 1979-09-27
Filing date: 1980-07-10
Publication date: 1981-04-08
Also published as: JPS5651381A; EP0026275A3; DE3066963D1; JPS585794B2; CA1143689A; EP0026275B1

Abstract

To provide an improved mechanical reversible spooling drive in a printer, a pair of spool spindles (32; 34), each carrying an apertured circular plate with peripheral ratchet teeth (32a; 32b: 34a; 34b) and a bail trigger (54: 55) spring loaded to extend through the aperture from one side thereof, are provided at the limits of the print path of a print head (24) driven reciprocally over the path. Print ribbon in the path is spooled on and between the spindles generally obstructing the apertures and restraining the triggers against the spring loading. Fixed abutments (52; 53) are engageable by a respective trigger when its spool is empty to lock that spindle and to engage, when the head is at the end of the path, a camming surface (64; 66) provided at each end of a bail (20) pivotally mounted on the print head and rendered positionally bistable by an overcentre mechanism (74) and place it in a position in which one of a pair of pawis (60;62) engage the ratchet teeth to spool ribbon onto the "empty" spindle each time the print head reaches that end of the print path.

Description

The invention relates to printers including a mechanism for driving a print ribbon to alternately wind the print ribbon, applied across the print head of the printer, alternately on one spool at one side in the machine and on an opposite spool at the other side of the machine.
Print ribbon driving mechanisms for alternately winding a print ribbon on opposite spools have been previously proposed which rely on the tension or resistance to further turning of a spool when unwound such as to cause a swing lever to be effective for winding the ribbon on an immediately depleted ribbon spool. An example of such a ribbon drive construction is disclosed in U. S. Patent 4,046,246 which discloses a swingable drive arm that is alternately effective for winding a print ribbon on one or the other of a pair of ribbon spools. Another example of such a ribbon drive construction is disclosed in U. S. Patent 3,880,271. The latter structure includes a swingable feed pawl beam which has two detented positions for this purpose in which its two notches alternately rest on a drive stud. The beam thus has two principal positions in each of which it drives one of a pair of ribbon spools. The International Business Machines Technical Disclosure Bulletin publication, Vol. 21, No. 9, February 1979, pages 3687 and 3688, discloses another example of such a structure. In this structure, a longitudinally movable shifting pawl is alternately effective to drive one or the other of two ribbon spool ratchets, and the mechanism is changed from a condition driving one of the ratchets to a condition driving the other ratchet by a shifter control which is responsive to the amount of ribbon on one of the spools. The shifter control drops when the ribbon is depleted on this spool to drive a detent bar from one position to another position to cause the shifting pawl to be changed in its operation to drive one of the ratchet wheels in lieu of the other.
There is a tendency for such mechanisms to tension the ribbon and to avoid this the present invention provides a printer of the kind in which, in operation, a print ribbon is spooled between a pair of spools respectively mounted on spindles located at the ends of a print path so that the ribbon lies along the print path, a print head being driven to and fro along the path and carrying a spool drive bail having two stable operative positions in each of which it is effective to drive a respective spool when the print head is at or near the end of the path adjacent that spool characterized in that the spindles each include a bail trigger loaded towards engagement with the spool drive bail and normally restrained against the loading by the side of a supply of print ribbon when such is present on the respective spool, the effect of an unrestrained trigger being to switch the bail, (if not already so positioned) to that one of its stable position in which it is effective to drive the spool associated with the unrestrained trigger, when the print head approaches that end of the print path.
Such an arrangement is an improvement in that it avoids certain operating problems resulting from the use of ribbon tension for causing ribbon reversal by being responsive only to the substantial absence of ribbon on one of two opposite ribbon spools without influence of ribbon tension to alternate the drive of the two spools so that a just depleted ribbon spool is driven in a ribbon winding direction. Other real and potential advantages are discussed hereinafter in connection with an embodiment of the invention as illustrated in the accompanying drawings in which :-

FIG. 1 is a plan view of one form of printer of the invention showing the print ribbon driving mechanism including a pair of ribbon spool carrying spindles, a trigger lever swingably mounted on each of the spindles and a switching bail swingably mounted on a reciprocative print head;
F_IG. 2 is an exploded perspective view of one of the spindles together with the trigger lever swingably mounted on the spindle;
FIG. 3 is a side elevational view of one of the spindles together with its trigger lever taken on the lines III-III of FIG. 1; and
FIG. 4 is a fragmentary perspective view of one of the trigger levers together with its support.

The printer of which only material parts are illustrated in Figure 1 includes a print head 24 capable of moving to and fro along a print path spanned by a print ribbon 26 carried between two spools 28 and 30.
The print ribbon driving mechanism includes a switching bail 20 which is oscillatably disposed on the carrier 22 of the print head 24. The print head 24 has a nose tip 24a, and the print ribbon 26 passes over the nose tip 24a. The ribbon 26 is disposed on the ribbon supply spools 28 and 30 and has its ends fixed to the spools. The spools 28 and 30 are disposed on the toothed spindles 32 and 34 respectively. The teeth on the spindle 32 have radially extending surfaces 32a and alternate surfaces 32b connecting the surfaces 32a and extending at an angle with respect to radial. The teeth on the spindle 34 have radially extending tooth surfaces 34a connected by alternate tooth surfaces 34b connecting the tooth surfaces 34a and extending at an angle with respect to radial. As the teeth are seen in plan in FIG. 1, it will be noted that the tooth surfaces 32b and 34b slant inwardly toward the centres of the spindles oppositely with respect to each other, and this is so that the radially extending tooth surfaces 32a and 34a are available for engagement by the bail 20 approaching the spindles 32 and 34 from opposite directions as will be apparent from subsequent description.
The carrier 22 is slideably disposed on a stationary carrier guide rod 36 so that the carrier 22 and thereby the print head 24 may reciprocate in directions 37 and 38. The print head 24 may thus provide lines of print on the printing medium 40 with the lines of print extending in directions 37 and 38. The print head 24 for this purpose may be of the wire type which includes wires 24b that are selectively thrust through the nose tip 24a to billow the ribbon 26 off the tip 24a and into contact with the medium 40 for printing corresponding dots on the medium 40. The carrier 22 is reciprocatively driven in directions 37 and 38 by any suitable motive means (not shown).
Spool brackets 42 and 44 are mounted to the frame 46 of the machine in which the print head 24 is installed, and brackets 42 and 44 respectively carry the spindle studs 48 and 50. The spool bracket 42 having the spindle stud 48 mounted thereon is shown in detail in FIG. 2, and the assembly of the spindle stud 50 on the spool bracket 44 is similar. The upper surface of the bracket 42 is embossed with a depression 51 providing a vertical shoulder 52, and a similar shoulder 53 is formed on the bracket 44. Spindles 32 and 34 have reversing trigger levers 54 and 55 swingably mounted on them. The levers 54 and 55 and their mountings on the tooth spindles 32 and 34 are similar, and the lever 54 together with its mounting is shown in detail in FIGs. 2, 3 and 4. The lever 54 is swingably mounted on the upstanding portion 56a of a bracket 56 fitting over stud 48 and extends upwardly through an opening 32a in spindle 32. The lever 54 has a toe portion 54a, and the tang 57a of a leaf spring 57 fitting over bracket 56 extends over the toe portion 54a for the purpose of providing a swinging force on the lever 54 tending to swing the lever 54 away from the centre line of the spindle 32 and stud 48 and urging the lever downwardly into engagement with the upper surface of the bracket 42. A drag spring 58 is attached to the bracket 42 and engages with the teeth of the associated spindle 32, and a similar drag spring (not shown) is used in connection with the spindle 34. Each of the spindles 32 and 34 is provided with a non-round exterior surface, and this surface corresponds with and mates with a corresponding non-round opening 28a in the spool 28 or 30a in the spool 30.
The bail 20 is provided with pawl surfaces 60 and 62 on opposite ends and with camming surfaces 64 and 66 on opposite ends. The bail 20 is swingably disposed on the carrier 22 by means of a pin 68, and a pin 70 extends through an opening 72 in the bail 20 for limiting the swinging movement of the bail 20. An overcentre spring 74 is provided effectively between the bail 20 and the carrier 22 for yieldably holding the bail 20 in either of its end positions limited by the pin 70.
In operation, the carrier 22 and the print head 24 are reciprocated in the opposite directions 37 and 38 so that the head 24 may print lines of print on the print medium 40. Initially, the bail 20 may be assumed to be in its position shown in FIG. 1, swung in the clockwise direction about the pin 68 to a limit determined by the pin 70. When the head 24 along with the carrier 22 moves in the direction 38 to complete a line of print on the medium 40 in this direction, the pawl surface 62 moves into engagement with one of the tooth surfaces 34a on the spindle 34 and thus rotates the spindle 34 about the spindle axis in the clockwise direction as seen in FIG. 1 for a certain arc, for example corresponding to four of the teeth on the spindle 34. The spool 30 has a non-rotative connection with the spindle 34, and the spool 30 thus rotates for the same arc of rotation. The ribbon 26 is fixed at its ends to the spools 28 and 30, and this rotation of the spool 30 thus winds the ribbon 26 onto the spool 30 and unwinds the ribbon from the spool 28 which rotates correspondingly and freely in the clockwise direction (see FIG. 1) about the axis of the spindle 32. The carrier 22 and print head 24 then reciprocate in the opposite direction 37 for printing a line of print in this direction; however, with the bail 20 being in its illustrated position of FIG. 1 with respect to the carrier 22, the pawl surface 60 is out of line with respect to and passes over and makes no contact with the teeth of the spindle 32. The spindle 32 and the spool 28 are thus not rotated with this reciprocation of the print head 24 and carrier 22 in direction 37. Each successive reciprocation of the print head 24 and bail 20 in the direction 38 winds a corresponding length of the ribbon 26 onto the spool 30, while the corresponding reciprocations in the direction 37 have no effect on the spindle 32 and spool 28.
When the ribbon 26 is depleted on the spool 28 until practically none of the ribbon remains on the spool 28, the trigger lever 54 is no longer held by the ribbon 26 on the spool 28 in the position of the lever 54 in which its lower end 54a is out of contact with the upper surface of the bracket 42. The lever 54 thus swings downwardly due to the action of the spring tang 57a, since the lever 54 is no longer held by the ribbon 26; and the lower end 54a of the lever 54 makes contact and rides on the upper surface of the bracket 42. On a final arc of rotation of the spindle 32 and spool 28 (in the ribbon unwinding clockwise direction as seen in FIG. 1), the lever end 54a moves downwardly into the depression 51 and strikes the shoulder 52 which prevents any further rotation of the spindle 32 and spool 28 about the axis of the spindle 32 in the clockwise direction as seen in FIG. 1. On the next succeeding reciprocation of the carrier 22 and bail 20 in the direction 37, the camming surface 64 strikes the lower end 54a of the trigger lever 54 in contact with the shoulder 52, and the bail 20 is thus swung in the counterclockwise direction about the pin 68 to the limit of its movement in this direction as limited by the pin 70. On subsequent movements of the carrier 22 and head 24 in the direction 37, the pawl surface 60 is then in place to strike a tooth surface 32a of the spindle 32, and the spindle 32 and the spool 28 are thus rotated in the counterclockwise direction as seen in FIG. 1 in order to wind the ribbon 26 onto the spool 28 with a corresponding unwinding of the ribbon 26 from the spool 30. The pawl surface 62, with the bail 20 being at the limit of its rotation in the counterclockwise direction as seen in FIG. 1, is out of line for engaging with the teeth of the spindle 34, and the spindle 34 and spool 30 thus have a free ribbon unwinding action. The lever 54 is swung upwardly out of engagement with the upper surface of the bracket 42 by the ribbon 26 as it winds on the spool 28.
Finally the ribbon will be depleted from the spool 30, and the trigger lever 55 will swing downwardly and engage the abutment surface 53 so as to hold the spool 30 and spindle 34 from any further unwinding action; and the cam surface 66 will strike the trigger lever 55 in contact with the shoulder 53 and will again swing the bail 20 back into its illustrated position in which the pawl surface 62 is effective on the teeth of the spindle 34 as above described.
These reciprocations of the bail 20 to the limits of its swinging movement by the actions of the camming surfaces 64 and 66 on the trigger levers 54 and 55 respectively as the ribbon 26 is depleted from one or the other of the spools 28 and 30 cause the ribbon 26 to be successively and alternately wound on the spools 30 and 28 from the other of the spools.
A printer with this kind of ribbon drive mechanism has numerous advantages. It is not dependent on the tension of the ribbon 26 for reversing the spooling actions of the spools 28 and 30 so that it is not subject to a potential blockage of ribbon movement for one reason or another which could cause an undesirable premature reversal of ribbon movement prior to an exhaustion of either one of the ribbon spools and so that the print wires 24b when a wire print head is used cannot be impeded in their movements toward the medium 40 by the ribbon 26 and possibly punch through the ribbon 26 and be prevented by the ribbon from full return movement with a disastrous ribbon and wire jam resulting. The ribbon drive mechanism does not require the use of sensing arms dragging on the ribbon 26 during spooling to change the winding direction which could cause undesired ribbon tension and which would have to be rotated out of the way manually when a new ribbon is installed in the machine. The ribbon loading path is simple particularly since the ribbon is not routed around such tension arms. The ribbon drive has few parts resulting in, potentially, a very low cost mechanism. It does not exert a drag on the carrier 22 for the print head 24 during printing. The tension on the ribbon 26 is not increased during reversing. The swingable bail 20 together with the carrier 22 and print head 24 as an assembly can be constructed to have a desirably low inertia.

Claims

1. A printer of the kind in which, in operation, a print ribbon (26) is spooled between a pair of spools (28; 30) respectively mounted on spindles (32; 34) located at the ends of a print path so that the ribbon lies along the print path, a print head (24) being driven to and fro along the path and carrying a spool drive bail (20) having two stable operative positions in each of which it is effective to drive a respective spool when the print head is at or near the end of the path adjacent that spool characterized in that the spindles (32; 34) each include a bail trigger (54; 55) loaded towards engagement with the spool drive bail (20) and normally restrained against the loading by the side of a supply of print ribbon when such is present on the respective spool, the effect of an unrestrained trigger being to switch the bail, (if not already so positioned) to that one of its stable position in which it is effective to drive the spool associated with the unrestrained trigger, when the print head approaches that end of the print path.

2. A printer as claimed in claim 1 characterized in that the bail (20) is pivotally mounted (at 68) on the print head, rendered bistable by an overcentre mechanism (74) and has a pawl (60; 62) and a camming surface (64; 66) at each side of the pivotal mounting arranged so that the pawl on one side and the camming surface on the opposite side of the pivotal mount are potentially available to engage respectively with one spool to drive the same and with the bail trigger of the other spool when unrestrained.

3. A printer as claimed in either preceding claim characterized in that each spindle (32; 34) is provided with ratchet teeth (32a; 32b: 34a; 34b) and a fixed abutment in a position to be engaged by the respective bail trigger when unrestrained to lock the spindle and define the position for engagement with the bail.

4. A printer as claimed in claim 3 characterized in that for each spindle, the ratchet teeth are formed on the periphery of a circular plate on one side of which the print ribbon is spooled, the plate being apertured and the trigger being urged by a spring (57) mounted on the reverse side of the circular plate to pass through the aperture when the aperture is not obstructed by a supply of ribbon.